Academic selection in England's schools has been replaced by social selection, a report warned today. Photograph: Don McPhee for the Guardian

In most areas of England, academic selection for grammar school was rightly abolished many years ago. It has been replaced, however, by something far more iniquitous: social selection, which excludes large numbers of impoverished children from hundreds of supposedly comprehensive schools. Academic selection at 11 is itself socially biased: middle-class children had a far better chance of a grammar school place, but at least a few raggedy-trousered diamonds got through. Now, the most deprived comprehensive has 16 times as many children from poor homes as the least deprived.

The situation is highlighted today by a report from Barnardo's, the children's charity. It argues that government policies, far from reducing segregation, are likely to accentuate it. This view is supported by a mountain of research. Ministers propose to open more of the academies that Labour pioneered (but with the difference that they will be already successful schools, given academy status as a perk, rather than conversions of struggling schools in deprived areas) and also to allow parents, teachers and voluntary groups to set up "free schools" with support from public funds.

Such schools, outside the local authority system, will control their own admissions, as voluntary-aided (mostly denominational) and foundation schools already do. The educational charity Sutton Trust has shown that, on average, the 42% of schools that control admissions have considerably lower proportions of children from income-deprived homes.

The admissions system is often described as a postcode lottery, allowing affluent parents to buy houses in the catchment areas of the "best" schools. But it is far more complex than that. According to Sutton Trust, in the 100 most socially selective comprehensives, the average proportion of children from income deprived homes is 8.6%, against 20.1% in the schools' localities. The middle classes will go to any lengths to get their children into favoured schools, including moving into temporary accommodation. The schools themselves, though bound by the government's fair admissions code, will do little to discourage parents who play the system. Almost by definition, such parents will be supportive and their children motivated. When a school's survival and its teachers' careers depend on league table positions, incentives to turn a blind eye are almost irresistible.

Segregation matters. Another mountain of research, covering countries across the developed world, shows overall levels of attainment rise where schools get a "balanced intake", with the proportions of children from deprived and affluent homes roughly reflecting their proportions in the general population.

Free schools will almost certainly want to get off on a sound footing by recruiting children from advantaged backgrounds. The Tories' proposals are modelled on Sweden, where free schools were set up by a rightwing government in the 1990s. The result was more social segregation – and a slide down international league tables of pupil attainment. Coalition ministers argue that the Lib Dems' favourite educational policy – the "pupil premium", which will give schools more money for each child recruited from a poor home – will ensure that doesn't happen here. But nobody yet knows how large the premium will be, and whether it will be enough to persuade schools actively to seek less-advantaged children.

Barnardo's is right to sound the alarm. Community schools – those still under local council control – are in danger of being reduced to a "sink" sector, where teachers struggle with low-attaining children from highly deprived backgrounds. The social segregation of England's schools will be complete.